Journal: Geomechanics and Geophysics for Geo-Energy and Geo-Resources

Abbreviation

Geomech. Geophys. Geo-energ. Geo-resour.

Publisher

Springer

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ISSN

2363-8427
2363-8419

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20222
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Publications 1 - 2 of 2
  • Spectral boundary integral method for simulating static and dynamic fields from a fault rupture in a poroelastodynamic solid
    Item type: Journal Article
    Heimisson, Elías Rafn; Rinaldi, Antonio Pio (2022)
    Geomechanics and Geophysics for Geo-Energy and Geo-Resources
    The spectral boundary integral method is popular for simulating fault, fracture, and frictional processes at a planar interface. However, the method is less commonly used to simulate off-fault dynamic fields. Here we develop a spectral boundary integral method for poroelastodynamic solid. The method has two steps: first, a numerical approximation of a convolution kernel and second, an efficient temporal convolution of slip speed and the appropriate kernel. The first step is computationally expensive but easily parallelizable and scalable such that the computational time is mostly restricted by computational resources. The kernel is independent of the slip history such that the same kernel can be used to explore a wide range of slip scenarios. We apply the method by exploring the short-time dynamic and static responses: first, with a simple source at intermediate and far-field distances and second, with a complex near-field source. We check if similar results can be attained with dynamic elasticity and undrained pore-pressure response and conclude that such an approach works well in the near-field but not necessarily at an intermediate and far-field distance. We analyze the dynamic pore-pressure response and find that the P-wave arrival carries a significant pore pressure peak that may be observed in high sampling rate pore-pressure measurements. We conclude that a spectral boundary integral method may offer a viable alternative to other approaches where the bulk is discretized, providing a better understanding of the near-field dynamics of the bulk in response to finite fault ruptures.
  • Impact of injection rate ramp-up on nucleation and arrest of dynamic fault slip
    Item type: Journal Article
    Ciardo, Federico; Rinaldi, Antonio Pio (2022)
    Geomechanics and Geophysics for Geo-Energy and Geo-Resources
    Fluid injection into underground formations reactivates preexisting geological discontinuities such as faults or fractures. In this work, we investigate the impact of injection rate ramp-up present in many standard injection protocols on the nucleation and potential arrest of dynamic slip along a planar pressurized fault. We assume a linear increasing function of injection rate with time, up to a given time t(c) after which a maximum value Q(m) is achieved. Under the assumption of negligible shear-induced dilatancy and impermeable host medium, we solve numerically the coupled hydro-mechanical model and explore the different slip regimes identified via scaling analysis. We show that in the limit when fluid diffusion time scale t(w) is much larger than the ramp-up time scale t(c), slip on an ultimately stable fault is essentially driven by pressurization at constant rate. Vice versa, in the limit when t(c)/t(w) >> 1, the pressurization rate, quantified by the dimensionless ratio Q(m)t(w)/t(c)Q* with Q* being a characteristic injection rate scale, does impact both nucleation time and arrest distance of dynamic slip. Indeed, for a given initial fault loading condition and frictional weakening property, lower pressurization rates delay the nucleation of a finite-sized dynamic event and increase the corresponding run-out distance approximately proportional to proportional to (Q(m)t(w)/t(c)Q*)^(-0.472). On critically stressed faults, instead, the ramp-up of injection rate activates quasi-static slip which quickly turn into a run-away dynamic rupture. Its nucleation time decreases non- linearly with increasing value of Q(m)t(w)/t(c)Q* and it may precede (or not) the one associated with fault pressurization at constant rate only.
Publications 1 - 2 of 2